During the drilling of deep wells, such as wells for producing petroleum products, objects such as drill pipe, tubing, well tools and other apparatus sometimes become stuck within the well bore and cannot be removed by application of ordinary upward force thereto. In such cases, it is frequently necessary to induce jarring forces to the stuck object in order to free it for extraction from the well bore. For purposes of this discussion, stuck objects are typically referred to in the industry as "fish," and operations that are conducted for removal of stuck or lost objects within a well bore are typically referred to as "fishing operations."
Jarring apparatus for inducing jarring forces to stuck objects take many different forms, depending upon the fishing operation to be conducted and typically involve two basic categories of jarring tools, i.e. hydraulically energized tools that are known as "oil jars" and mechanical jars. It is commonly known by all operators of deep well drilling and completion equipment that have had experience with any size oil jar on fishing operations in wells, that each well, having different characteristics, such as downhole pressure, hydrostatic head, temperature, friction, pipe stretch, deviated holes, etc., must be treated in specifically designed manner in order to accomplish an efficient fishing operation. Even fishing operations conducted in wells that are closely spaced and extend to a common oil producing subsurface formation have different characteristics that affect the function of oil jar mechanisms. It has been accepted by the well surface industry that it is practically impossible to calculate many of the foregoing well conditions and determine accurately the particular degree of energy stroke that is being imparted from an oil jar to a fish in any particular circumstance. For example, each well will have a particular bottom hole temperature that may be different from other wells and changes the density and viscosity of the oil within which the oil jar is located. Oil at higher temperature, of course, will be thinner and the viscosity thereof will be typically decreased at higher temperature ranges. In well bores that are more deviated, friction between the well bore and operating pipe or wire line typically increases and must be taken into consideration during fishing operations in order to determine the amount of force that is being applied through the oil jar mechanism. Further, where deep well bores are involved, the pipe or cable that supports the oil jar mechanism and the fishing tool will tend to have greater stretch simply due to the weight of the pipe or cable itself. When upwardly directed jarring forces are being applied through the supporting pipe or cable by surface control, the pipe or cable must be moved sufficiently to accommodate pipe stretch and yet apply a particularly designed jarring force to the fish.
A further disadvantage that is encountered through the use of oil jar mechanisms is the requirement to control the oil displacement that occurs within the oil jar tool. Under circumstances where oil jar mechanisms are closed rapidly, it is possible for the internal pressure within certain chambers of the oil jar to increase sufficiently to rupture the oil jar housing structure. From an operational standpoint, it is required that oil jars be carefully and slowly closed in order to induce slow displacement of the oil and thus eliminate the possibility of pressure energized rupture or explosion of the middle body on the oil jar. When operating an oil jar mechanism in a deep well where extensive cable or tubing stretch is involved, it is extremely difficult to accomplish slow closing of the oil jar mechanism. It is thus desirable to provide a fishing jar mechanism that can be opened and closed at any desirable speed without altering the characteristics of the energy stroke that is delivered to the fish.